Bowstring having different ultra high molecular weight polyethylene fibers for creep reduction

Abstract

A bowstring including first and second ultra high molecular weight polyolefin fibers is described herein. The first and second ultra high molecular weight polyolefin fibers have different compositions such that the first ultra high molecular weight polyolefin fibers have a greater elasticity than the second ultra high molecular weight polyolefin fibers.

The following is claimed: 
     
       1. A bowstring comprising:
 a first ultra high molecular weight polyolefin fiber comprising a first elasticity associated with a manufacturing contraction reduction characteristic; 
 a second ultra high molecular weight polyolefin fiber in contact with the first ultra high molecular weight polyolefin, the second ultra high molecular weight polyolefin comprising a second elasticity associated with an operational contraction enhancement characteristic, wherein the second elasticity is at least 5 percent greater than the first elasticity; and 
 a serving material applied to the first and second ultra high molecular weight polyolefin fibers when the first and second ultra high molecular weight polyolefin fibers are under a manufacturing tension so as to set the bowstring, 
 wherein, when the first and second ultra high molecular weight polyolefin fibers are under the manufacturing tension, a segment of the bowstring comprises an initial length, 
 wherein, when the manufacturing tension is removed and the bowstring is set, the segment comprises a return length, 
 wherein the return length differs from the initial length by less than 0.10 percent as a result of the manufacturing contraction reduction characteristic, 
 wherein, when the bowstring is set, installed on a bow and subject to an operational tension, the second ultra high molecular weight polyolefin fiber is configured to decrease an accumulation of slack in the bowstring, 
 wherein the decrease in the accumulation of slack is a result of the operational contraction enhancement characteristic. 
 
     
     
       2. The bowstring of  claim 1 , wherein the first elasticity and the second elasticity differ by at least 10 GPa. 
     
     
       3. The bowstring of  claim 1 , further comprising a stretched polytetrafluoroethylene fiber. 
     
     
       4. The bowstring of  claim 1 , further comprising a third ultra high molecular weight polyolefin fiber comprising a third elasticity, the third elasticity being at least 5 GPa different than each the first elasticity and the second elasticity. 
     
     
       5. The bowstring of  claim 4 , further comprising a liquid crystal polymer fiber. 
     
     
       6. The bowstring of  claim 5 , further comprising a stretched polytetrafluoroethylene fiber. 
     
     
       7. The bowstring of  claim 1 , further comprising a liquid crystal polymer fiber and a stretched polytetrafluoroethylene fiber. 
     
     
       8. The bowstring of  claim 7 , further comprising a plurality of strands twisted about each other, at least one of the strands comprising the first ultra high molecular weight polyolefin fiber and the second ultra high molecular weight polyolefin fiber. 
     
     
       9. The bowstring of  claim 1 , wherein the second elasticity is greater than 135 GPa and the first elasticity is less than 135 GPa, and the first elasticity and the second elasticity differ by at least 10 GPa. 
     
     
       10. The bowstring of  claim 1 , wherein the second elasticity is at least 10 percent greater than the first elasticity. 
     
     
       11. The bowstring of  claim 1 , wherein the second elasticity is at least 15 percent or 20 percent greater than the first elasticity. 
     
     
       12. The bowstring of  claim 1 , wherein the return length is identical to the initial length. 
     
     
       13. A bowstring comprising:
 a plurality of strands twisted together to form the bowstring, each one of the strands comprising:
 a plurality of first ultra high molecular weight polyethylene fibers; and 
 a plurality of second ultra high molecular weight polyethylene fibers, 
 
 wherein each of the plurality of first ultra high molecular weight polyethylene fibers has a first elasticity that is at least 5 percent greater than a second elasticity of each of the plurality of second ultra high molecular weight polyethylene fibers. 
 
     
     
       14. The bowstring of  claim 13 , wherein the first elasticity is between about 135 and 145 GPa and the second elasticity is between about 100 GPa and 135 GPa, and the first elasticity and the second elasticity differ by at least 5 GPa. 
     
     
       15. The bowstring of  claim 14 , wherein at least one of the strands comprises a stretched polytetrafluoroethylene fiber. 
     
     
       16. The bowstring of  claim 15 , wherein the plurality of first ultra high molecular weight polyethylene fibers is 61±3% m/m of the twisted strands, the plurality of second first ultra high molecular weight polyethylene fibers is 26±3% m/m of the twisted strands, and the stretched polytetrafluoroethylene fiber is 13±3% m/m of the twisted strands. 
     
     
       17. The bowstring of  claim 13 , further comprising a plurality of third ultra high molecular weight polyethylene fibers, each having a third elasticity, the third elasticity being at least 5 GPa different than each of the first elasticity and the second elasticity. 
     
     
       18. The bowstring of  claim 17 , wherein at least one of the first ultra high molecular weight polyethylene fibers is 70±3% m/m of the twisted strands, at least one of the second ultra high molecular weight polyethylene fibers is 15±3% m/m of the twisted strands and at least one of the third ultra high molecular weight polyethylene fibers is 15±3% m/m of the twisted strands. 
     
     
       19. The bowstring of  claim 17 , further comprising:
 a plurality of liquid crystal polymer fibers; and 
 a plurality of stretched polytetrafluoroethylene fibers. 
 
     
     
       20. The bowstring of  claim 19 , wherein:
 the first ultra high molecular weight polyethylene fibers, the second ultra high molecular weight polyethylene fibers, the third ultra high molecular weight polyethylene fibers, and the plurality of liquid crystal polymer fibers are each present in equal proportions by mass of one unit of one of the strands within ±3%; 
 the unit has a total weight; and 
 the plurality of stretched polytetrafluoroethylene fibers provide a balance of the total weight less an aggregate weight of the first ultra high molecular weight polyethylene fibers, the second first ultra high molecular weight polyethylene fibers, the third ultra high molecular weight polyethylene fibers, and the plurality of liquid crystal polymer fibers. 
 
     
     
       21. The bowstring of  claim 19 , wherein each of the first ultra high molecular weight polyethylene fibers is 31±3% m/m of the strands, each of the second ultra high molecular weight polyethylene fibers is 31±3% m/m m/m of one of the strands, each of the plurality of liquid crystal polymer fibers is 23±3% m/m of one of the strands and each of the stretched polytetrafluoroethylene fibers is 15±3% m/m of one of the strands. 
     
     
       22. The bowstring of  claim 19 , wherein each of the first ultra high molecular weight polyethylene fibers is 33±3% m/m of one of the strands, each of the second ultra high molecular weight polyethylene fibers is 33±3% m/m of one of the strands, the plurality of liquid crystal polymer fibers is 17±3% m/m of one of the strands, and the plurality of stretched polytetrafluoroethylene fibers is 17±3% m/m of one of the strands. 
     
     
       23. A bowstring produced through a method, the method comprising:
 forming a plurality of first ultra high molecular weight polyolefin fibers; 
 forming a plurality of second ultra high molecular weight polyolefin fibers,
 wherein each one of the plurality of first ultra high molecular weight polyolefin fibers has a first elasticity associated with a contraction reduction effect, 
 wherein each one of the plurality of second ultra high molecular weight polyolefin fibers has a second elasticity associated with a contraction enhancement effect, wherein the second elasticity is greater by at least 5 percent than the first elasticity; 
 
 combining a plurality of the first ultra high molecular weight polyolefin fibers with a plurality of the second ultra high molecular weight polyolefin fibers to form a first strand; 
 combining a plurality of the first ultra high molecular weight polyolefin fibers with a plurality of the second ultra high molecular weight polyolefin fibers to form a second strand; 
 tensioning the first and second strands to a predetermined tension to produce pre-tensioned strands; 
 twisting the pre-tensioned strands together at a predetermined pitch to produce a pre-tensioned, twisted strand assembly having an initial length; 
 applying one or more servings to the first and second strands before or after the tensioning step; and 
 releasing the predetermined tension, wherein after the predetermined tension is released, the contraction reduction effect prevents the twisted strand assembly from having a return length that differs from the initial length by over 0.10 percent. 
 
     
     
       24. The bowstring of  claim 23 , wherein:
 as a result of the contraction reduction effect, the twisted strand assembly is operable to reduce creep in the bowstring after the predetermined tension is released; and 
 as a result of the contraction enhancement effect, the twisted strand assembly is operable to decrease an accumulation of slack in the bowstring when the bowstring is installed on a bow and repeatedly retracted and released in use.